The present invention relates to a communication method and radio network control device in a mobile communication system.
The present invention is particularly suited for use in a mobile communication system in which data is copied at a mobile station, after which that copied data is sent to a plurality of base stations, then each base station sends that copied data directly or by way of a drift radio network control device (D-RNC) to a serving radio network control device (S-RNC), after which the S-RNC selectively combines and outputs a plurality of received data.
A mobile communication system such as W-CDMA is a radio communication system in which the wired portion and radio portion of a communication area are shared by a plurality of users, and as shown in FIG. 10, includes: a core network (CN) 1; radio network control devices (RNC: Radio Network Controllers) 2, 3; radio base stations (Nodes B) 41 to 43, 51 to 53; and mobile stations (UE: User Equipment) 61 to 63. A radio network controller RNC is connected with a radio base station Node via an ATM network or IP network using a wired connection, and a radio base station (Node B) is connected with a mobile station UE by a radio connection.
The core network 1 is a network for performing routing in the mobile communication system, and it can comprise: an ATM switching network, packet switching network, router network, and the like. The core network 1 can also be connected to other public networks (PSTN) such that the mobile stations 61 to 63 are capable of performing communication with fixed telephones and the like.
The radio network devices (RNC) 2, 3 are positioned as host devices to the radio base stations (hereafter referred to as base stations) 41 to 43, 51 to 53, and perform control of these base stations (management of radio resources that are used by the base stations, etc.). Moreover, the RNC 2, 3 also comprise a selective combination function that receives identical data from a mobile station 6i via the plurality of subordinate base stations, selects data with the best quality, and outputs that data to the core network 1 side. The base stations 41-43 and 51-53 perform radio communication with a mobile station 6i, where RNC 2 manages the radio resources for the base stations 41 to 43, and RNC 3 manages the radio resources for the base stations 51 to 53. When a mobile station 6i enters the radio communication area of a base station, the mobile station 6i establishes a radio communication line with that base station, and performs communication with another communication device via the core network 1.
Iur is regulated as the interface between the core network and a RNC, Iur is regulated as the interface between a pair of RNC, Iub is regulated as the interface between a RNC and each of the base stations, and Uu is regulated as the interface between a base station and a mobile station.
In the mobile communication system described above, it has been proposed that in order for high-speed data transmission to be possible in the downlink direction, the HSDPA (High Speed Downlink Packet Access) method be employed, and that in order for high-speed data transmission to be possible in the uplink direction, the HSUPA (High Speed Uplink Packet Access) method be employed (refer to 3GPP TS 25.321 V7.30). The HSUPA method is a broadband data transmission function comprising an E-DCH (Enhanced Dedicated Transport Channel) for the purpose of improving the performance of individual channels DCH (dedicated channels) when a mobile station transmits data in the uplink direction.
FIG. 11 is a drawing explaining the transmission paths of uplink traffic when HSUPA is applied to a standard W-CDMA system, where there is a plurality of transmission paths (branches) formed between a mobile station 6 and a serving radio network controller (S-RNC) 2. The mobile station 6 copies the data to be transmitted and distributes the copied data to a plurality of base stations (Nodes B) 41 to 43. When doing this, the mobile station 6 attaches a TSN (Transmission Sequence Number) to each copy of data to indicate the transmission order of the data. In other words, as shown in FIG. 12, when the mobile station 6 transmits data Xn to the core network 1, the mobile station 6 makes copies of that data Xn equal to the number of paths (3 copies in the figure), attaches the same transmission sequence number TSN to each copy of the data Xn and distributes the data to a plurality of base stations using an independent communication method (for example changes the spreading code). Each transmission path is formed by the radio zone between the mobile station and the base station, and the inter-station line (Iub) between the base station and the S-RNC, such that the copied data is finally brought together at the S-RNC 2 via each of the transmission paths. The S-RNC receives the copied data Xn via each respective path, then selectively combines the data by referencing and rearranging the TSN, and sends the selectively combined data to the core network CN. By having redundancy of transmission paths in this way, even when there may be a drop in transmission quality in each branch or there may be a missing frame, the HSUPA method is designed to reduce effects thereof and maintain overall transmission quality.
FIG. 13 is a drawing showing the layered structure (protocol stack) of each unit in the HSUPA method, where the mobile station (UE) comprises a physical layer (PHY) in layer L1, and MAC sub-layers (MAC-d, MAC-es/MAC-e) in layer L2. The MAC sub-layers include a MAC-d (MAC dedicated) layer, MAC-e (MAC enhanced) layer, and MAC-es (MAC enhanced sub-layer). The base station (Node B) comprises a physical layer (PHY) for communicating with the mobile station according to the Uu interface, and a TNL layer (Transport Network Layer) for packet communication with the radio network controller (RNC) according to the Iub interface, and further comprises a MAC-e layer and EDCH FP (Enhanced DCH Frame Protocol) layer. The radio network controller (RNC) comprises a TNL layer, EDCH FP layer, MAC-es layer and MAC-d layer.
FIG. 14 is a drawing explaining the procedure by the mobile station for creating data TRB (transport block MAC-e PDU). First, the mobile station 6 uses data that is sent via a dedicated channel such as DTCH (Dedicated Traffic Channel) or DCCH (Dedicated Control Channel) and creates a data packet (MAC-d PDU data) for the MAC-d layer. This MAC-d PDU data is the same as the data packet (RLC PDU) data) of the RLC sub-layer. Next, the mobile station multiplexes some MAC-d PDU data, and attaches a transmission sequence number TSN at the start of the data to create data (MAC-es PDU) for the MAC-es layer. After that, the mobile station multiplexes a plurality of these MAC-es PDU data, and attaches a MAC-e header to the start of that data to create data (MAC-e PDU) for the MAC-e layer, then sends this data to the base station according to the Uu interface as a transport block TRB. The MAC-e header is a header that specifies the DDI (Data Description Identifier) and N for each MAC-es PDU data, where N specifies the number of MAC-d PDU data that are included in MAC-es PDU data, and DDI specifies the size and ID of each MAC-d PDU data.
FIG. 15 is a drawing explaining the multiplexing relationship of the MAC-d PDU, MAC-es PDU and MAC-e PDU data, where N1 number of MAC-d PDU data are multiplexed to form one MAC-es PDU data, and n number of MAC-es PDU data are multiplexed to form one MAC-e PDU data.
After receiving a transport block (MAC-e PDU) from the mobile station, the base station creates an EDCH Iub FP frame according to the EDCH FP protocol and sends that EDCH Iub FP frame to the RNC in the TNL layer. That is, the base station adds a header CRC, FSN (Frame Sequence Number), CFN (Connection Frame Sequence), number of MAC-es PDU data, and the like to the header of the MAC-e PDU data to create an EDCH Iub FP frame.
When the RNC receives an EDCH Iub FP frame for each logical channel, the RNC performs the reverse operation as the mobile station by reference to the MAC-e header, separates the MAC-e PDU data into MAC-es PDU data, and then further separates the MAC-es PDU data into MAC-d PDU data. Next, since there is a plurality of paths between the RNC and UE, the RNC selectively combines and rearranges the data received through each of the paths by referencing the transmission sequence numbers TSN that were attached at the time the mobile station transmitted the data, then gives the combined and rearranged MAC-d PDU data to the RLC sub-layer and transmits the dedicated channel data to the core network via that RLC sub-layer.
FIG. 11 described above is the most typical example of the application of the HSUPA method, however, as the mobile station moves, the copied data from that mobile station often arrives at the S-RNC 2 after first passing through a drift RNC (D-RNC) other than that S-RNC 2. FIG. 16 is a drawing explaining that transmission path, and shows the case in which the mobile station 6 moves from the state shown in FIG. 11 and transmits copied data to the S-RNC 2 via the base stations 51 and 52 that are subordinate to a drift RNC (D-RNC) 3 other than the S-RNC 2. In this case, each copied data that is transmitted from the mobile station 6 to the base stations 51 and 52 arrives at the S-RNC 2 via the inter-station line (Iur) between the D-RNC and S-RNC. The S-RNC 2 by referencing the TSN, rearranges the copied data that was received via that line (Iur) and the copied data that was received from the base station 43 via the other line (Iub) and selectively combines the copied data, then sends the selectively combined data to the core network CN.
As was described above, the HSUPA method, which is based on the distribution of the copied data and selective combination of data, has redundancy in the E-DCH (Enhanced Dedicated Transport Channel) traffic. This redundancy is useful from the aspect of maintaining the transmission quality that is provided to the mobile station; for example, it is possible to improve the transmission quality that can be provided to the mobile station more the higher the redundancy is improved by increasing the number of branches or the like. However, on the other hand, the allowable bandwidth for each of the lines of the transmission path is limited, while at the same time, the required cost that corresponds to the size of that allowable bandwidth also increases. Particularly, in the case of traffic of an E-DCH frame, whose absolute amount itself is large when compared with other traffic, it is feasible that the bandwidth of the lines of the transmission path will be greatly stressed due to that redundancy.
When the lines of the transmission path become congested and the amount of flow over the lines finally exceeds the allowable bandwidth, the frames on that transmission path are discarded, which not only affects on the E-DCH transmission quality, but also has an unpredictable adverse effect on other traffic that passes over the same path. Therefore, the occurrence of such a condition much be avoided as much as possible.
Incidentally, as shown in FIG. 16, there is a possibility that redundant traffic will become extremely concentrated in the line (Iur) that connects between the D-RNC and S-RNC. In the case shown in FIG. 16, there are two branches that pass through the D-RNC, so in the case in which the transmission condition of each of the branches is ideal, two EDCH frames having the same content are transmitted over the same physical line (Iur), and finally, as a result, one is selected by the selective combination that is performed by the S-RNC, and the other frame is discarded. In other words, the traffic that flows over the Iur line is double the traffic that flows over the Iub line, and as a result half of that traffic becomes useless.
A COMA mobile system has been proposed that minimizes the waiting delay for performing the selective combination process by the RNC (refer to Japanese patent application 2001-25046). In this related art, the RNC comprises a through mode in which received uplink data is sent to the core network as is without being stored in a buffer, and when there is only one uplink communication connection, received uplink data is sent by the through mode to the core network without waiting for the selective combination process, and by doing so, minimizes the wait delay for the selective combination process. However, in this related art, when there is a plurality of communication connections, and especially when the radio base station controller on the drift side is included in the path, the radio base station controller (D-RNC) performs always normal selective combination, and redundancy of the transmission path is always lost.